Unity Gif to Sprite Sheet Converter

Further recommendations

After importing the result image in unity don't forget to change settings for the texture.
Texture Type - Sprite (2D and UI)
Sprite Mode - Multiple
Alpha Is Transparency - ☑
Compression - None
Then press Apply

After that you can slice your sprite sheet
Press button Sprite Editor
Select Slice
Type - Grid By Cell Count
Column & Row - C: !F(frames total) R: 1
Press Slice
And don't forget to press Apply

Now you can close sprite editor and your sprite sheet is ready to use!